The effects of strain-rate variations on the flow stress of OFHC copper

T he response of OFHC copper to a dynamic strain-rate reduction was determined from experiments which employed a modified torsional split Hopkinson bar apparatus. In these experiments the initial specimen strain rate was approximately 10 3 sec −1, and it was held nearly constant for about 200 μsec before being reduced to approximately 10 2 sec −1. The material behavior under these conditions was found to be strain-rate history dependent, so that a mechanical equation-of-state of the Zener-Hollomon type does not provide an adequate description of the specimen response. In addition, the experimental evidence suggests that an unstable microstructure may be formed as a result of this strain-rate history.